Trellis: Robust and Scalable Metadata-private Anonymous Broadcast

Langowski, Simon; Servan-Schreiber, Sacha; Devadas, Srinivas

doi:10.14722/ndss.2023.23088

Cited by 5 publications

(5 citation statements)

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“…Pairwise unlinkability is close to message indistinguishability properties from the literature, such as tail indistinguishability by Kuhn et al [17]. Capturing privacy-related notions via indistinguishability of two messages is commonly used by other provably secure designs [4,7,10,19,20]. We present our definition via the corresponding game described in Figure 4.…”

Section: Pairwise Unlinkability Definitionmentioning

confidence: 93%

“…Even though continuous mixnets are around for more than two decades [16], it was not yet known if they can provide provable anonymity guarantees. Existing mixnet designs [1,10,19,20,22,28,29] that attempt to provide provable anonymity guarantees mainly rely on (1) batch processing, and (2) round based communication model. Because of the round based communication model, all the messages that arrive to an honest mixnode in a given round are shuffled by the mixnode and forwarded to the next mixnodes/destination.…”

Section: Related Work and Challengesmentioning

confidence: 99%

“…Anonymous communication (AC) protocols based on mixnets [1,3,4,10,19,21,23,29] aim to provide anonymity by rerouting packets over several hops and adding delays on every hop of messages that allow the messages to mix with each other. All mixnets that attempt to provide provable anonymity guarantees do so by relying on some kind of round based communication model [1,10,19,20,29] -it is difficult to implement such round structure in practice when there are thousands of nodes and millions of clients in the system. Continuous stop-and-go mixnets (or simply, continuous mixnets) [11,16,26] avoid such round-based communication by adding a random delay (chosen from a predefined distribution) on every hop of each message, independent of all other hops of the message as well as independent of all other messages.…”

Section: Introductionmentioning

confidence: 99%

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Are continuous stop-and-go mixnets provably secure?

Das,

Diaz,

Kiayias

et al. 2024

PoPETs

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This work formally analyzes the anonymity guarantees of continuous stop-and-go mixnets and attempts to answer the titular question. Existing mixnet based anonymous communication protocols that aim to provide provable anonymity guarantees rely on round-based communication models, which requires synchronization among all the nodes and clients that is difficult to achieve in practice. Continuous stop-and-go mixnets (e.g., Loopix and Nym) provide a nice alternative by adding a random delay for each message on every hop independent of all other hops and all other messages. The core anonymization technique of continuous mixnets combined with the fact that the messages are sent by the clients to the mixnet at different times makes it a difficult problem to formally prove security for such mixnet protocols; existing end-to-end analyses for such designs provide only experimental evaluations for anonymity and were lacking a comprehensive formal treatment. We are the first to close that gap and provide a formal analysis. We provide two indistinguishability based definitions (of sender anonymity), namely pairwise unlinkability and user unlinkability, tuned specifically for continuous stop-and-go mixnets. We derive the adversarial advantage as a function of the protocol parameters for the two definitions. We show that there is a fundamental lower bound on the adversarial advantage $\delta$ for pairwise unlinkability; however, strong user unlinkability (negligible adversarial advantage) can be achieved if the users message rate ($\lambda_u$) is proportional to message processing rate ($\lambda$) on the nodes.

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Section: Pairwise Unlinkability Definitionmentioning

confidence: 93%

Section: Related Work and Challengesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Are continuous stop-and-go mixnets provably secure?

Das,

Diaz,

Kiayias

et al. 2024

PoPETs

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“…Cai et al [29] designed a metadata-hiding data analytic system called Vizard using the distributed point function, which allows data owners to share their data in a privacy-preserving manner, and the experimental results proved the practicality of the scheme. Langowski et al [30] designed a metadata-private anonymous broadcasting scheme called Trellis based on boomerang encryption and anonymous routing tokens that hides all network-level metadata and supports horizontal scalability. However, these solutions are designed for large network systems and are difficult to apply directly to edge systems with limited computational and bandwidth resources.…”

Section: Related Workmentioning

confidence: 99%

Metadata-Private Resource Allocation in Edge Computing Withstands Semi-Malicious Edge Nodes

Zhang,

Li,

et al. 2024

Sensors

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Edge computing provides higher computational power and lower transmission latency by offloading tasks to nearby edge nodes with available computational resources to meet the requirements of time-sensitive tasks and computationally complex tasks. Resource allocation schemes are essential to this process. To allocate resources effectively, it is necessary to attach metadata to a task to indicate what kind of resources are needed and how many computation resources are required. However, these metadata are sensitive and can be exposed to eavesdroppers, which can lead to privacy breaches. In addition, edge nodes are vulnerable to corruption because of their limited cybersecurity defenses. Attackers can easily obtain end-device privacy through unprotected metadata or corrupted edge nodes. To address this problem, we propose a metadata privacy resource allocation scheme that uses searchable encryption to protect metadata privacy and zero-knowledge proofs to resist semi-malicious edge nodes. We have formally proven that our proposed scheme satisfies the required security concepts and experimentally demonstrated the effectiveness of the scheme.

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“…Trellis [41] (2022) introduces an anonymous broadcast system that is robust to server churn. Their work, however, assumes a synchronous communication network and user liveness (i.e., all users are online for all rounds of communication).…”

Section: Mixnet Based Systemsmentioning

confidence: 99%

SoK: Metadata-Protecting Communication Systems

Sasy,

Goldberg

2024

PoPETs

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Protecting metadata of communications has been an area of active research since the dining cryptographers problem was introduced by David Chaum in 1988. The Snowden revelations from 2013 resparked research in this direction. Consequently over the last decade we have witnessed a flurry of novel systems designed to protect metadata of users' communications online. However, such systems leverage different assumptions and design choices to achieve their goal; resulting in a scattered view of the desirable properties, potential vulnerabilities, and limitations of existing metadata-protecting communication systems (MPCS). In this work we survey 31 systems targeting metadata-protected communications, and present a unified view of the current state of affairs. We provide two different taxonomies for existing MPCS, first into four different categories by the precise type of metadata protections they offer, and next into six families based on the core techniques that underlie them. By contrasting these systems we identify potential vulnerabilities, as well as subtle privacy implications of design choices of existing MPCS. Furthermore, we identify promising avenues for future research for MPCS, and desirable properties that merit more attention.

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Trellis: Robust and Scalable Metadata-private Anonymous Broadcast

Cited by 5 publications

References 0 publications

Are continuous stop-and-go mixnets provably secure?

Are continuous stop-and-go mixnets provably secure?

Metadata-Private Resource Allocation in Edge Computing Withstands Semi-Malicious Edge Nodes

SoK: Metadata-Protecting Communication Systems

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